The invention relates to a plasma spray method for the manufacture of an ion conducting membrane, in particular of a hydrogen ion conducting membrane or of an oxygen ion conducting membrane, and to an ion conducting membrane itself, in particular a hydrogen ion conducting membrane or an oxygen ion conducting membrane.
Ion conducting membranes are membranes that have a high selective permeability for specific ions. Oxygen permeable membranes are layers which have a high selective permeability for oxygen or oxygen ions and are substantially impermeable for other gases or ions. Correspondingly, such membranes are used in order to extract or to purify oxygen from gas mixtures or from fluid mixtures. The same is true for hydrogen permeable membranes for the extraction of hydrogen from gas mixtures or from fluid mixtures.
Such membranes can be manufactured from different materials. They can, for example, be composed of complex oxide materials which have a specific chemical composition and form specific phases. In particular, ceramic membranes are known which are composed of oxides of the perovskite type and which are manufactured in the form of thin, dense—this means non-porous—layers. Such membranes, for example, have both an ion conductivity for oxygen or hydrogen and also have an electron conductivity.
A material that is investigated and used today for the manufacture, in particular of oxygen permeable membranes is a ceramic material which has a perovskite structure and includes the elements lanthanum (La), strontium (Sr), cobalt (Co), and iron (Fe) besides oxygen. The substance is typically referred to as LSCF in accordance with the respective first letters of these four elements.
Oxygen permeable or hydrogen permeable membranes or generally ion conducting membranes of such materials can, for example, be manufactured by means of conventional manufacturing techniques for ceramics, such as, for example, pressing, tape casting, slip casting, or sintering or also by means of thermal spraying. In particular, thermal spray processes are suitable for the latter which are carried out in a vacuum. This typically means that the spray process is carried out at a process pressure that is smaller than the environmental pressure (normal air pressure)
A thermal low pressure plasma spray process or a vacuum plasma spray process is in particular suitable which is referred to as LPPS method (low pressure plasma spraying). By means of this vacuum plasma spray method particularly thin and dense layers can be sprayed particularly well, i.e., such layers which are also required for an ion conducting or oxygen permeable or hydrogen permeable membrane.
In this connection, the ion conducting membrane is deposited as a layer on a substrate in a process chamber. For this purpose, starting material is sprayed onto a surface of the substrate by means of a process gas in the form of a process beam. The starting material is injected into a plasma at a low process pressure which, for example, is at most 10,000 Pa and is partially or completely melted there.
During an LPPS method the ion conducting membrane is deposited on a substrate in the form of a layer. The substrate generally serves the purpose of supporting the thereby arising very thin and brittle layer and to thus make it manageable.